Gaseous fuels are employed to fuel internal combustion engines. In some applications, when there is a need to store a large quantity of fuel, and when there is limited space for storing such fuel, for example on board a vehicle, it is known to increase fuel storage density, thereby increasing vehicle operating range, by storing gaseous fuels, like natural gas, in liquefied form (LNG). A cryogenic storage vessel can typically store about four times more fuel compared to a like-sized storage vessel containing compressed natural gas (CNG). To deliver the gaseous fuel to the engine, a cryogenic pump is employed to pressurize the gaseous fuel to injection pressure, while it is still in liquefied form. The fuel is typically vaporized after being pumped so it is no longer in liquefied form when it is delivered to the engine. The delivery pressure can be within a wide range of pressures depending upon the design of the engine, and whether the downstream injection system is a low pressure or high pressure injection system. For example, among other factors, the delivery pressure depends upon whether the fuel is introduced into the intake air system, or directly into the combustion chamber, and if into the combustion chamber, the timing when it is introduced.
In known systems, the cryogenic pump can be situated in an external sump separate from the cryogen space defined by the cryogenic storage vessel, or can be installed with the pump assembly extending into the cryogen space as disclosed in the Applicant's co-owned U.S. Pat. No. 7,293,418. There are several advantages to installing the cryogenic pump assembly with the pump portion immersed in the liquefied gas and the drive portion on the outside of the cryogen space, including reduced start time for the pump, because unlike external pumps, which require time to be cooled to cryogenic temperatures to operate efficiently a pump that is located inside the cryogen space is maintained at cryogenic temperatures so long as there is liquefied gas stored inside the cryogenic vessel. In addition, when an external sump is connected to the cryogen space by piping such piping must be thermally insulated to reduce heat leak and vaporization of the liquefied fuel before it flows to the sump and then eventually to the pump.
A gaseous fuel is any fuel that is in a gaseous state at standard temperature and pressure, which in the context of this application is 20 degrees Celsius (° C.) and 1 atmosphere (atm). By way of example, typical gaseous fuels that can be stored in liquefied form include, without limitation, natural gas, propane, hydrogen, methane, butane, ethane, other known fuels with similar energy content, and mixtures including at least one of these fuels. Natural gas itself is a mixture, and it is a popular gaseous fuel for internal combustion engines because it is abundant, less expensive and cleaner burning than oil-based liquid fuels, and the sources are broadly dispersed geographically around the world. A purified form of LNG previously used in experimental railroad applications is referred to as refrigerated liquid methane (RLM).
In high horsepower applications, such as marine, mining and railroad applications, the quantity of fuel consumed by each engine, compared to an engine used for trucking applications is considerably greater. Accordingly, applications that consume more fuel require larger fuel storage vessels. As an example, a tender car comprising a cryogenic storage vessel for a locomotive can carry over 27,000 gallons of liquefied natural gas (LNG), compared to a typical 150 gallon capacity for a cryogenic storage vessel employed on a heavy duty truck. In trucking applications, when the cryogenic pump requires servicing, the storage vessel can be drained when the pump is removed. In high horsepower applications because of the much larger size of the fuel storage vessel and the much larger amount of liquefied fuel that can be stored therein, it is impractical, time consuming, and expensive to drain the liquefied fuel from the cryogenic storage vessel when the cryogenic pump must be removed for servicing.
The high horsepower internal combustion engines described above employ a maximum fuel flow rate that is considerably greater compared to heavy duty engines used for on-highway trucks. As an example, in certain applications a cryogenic pump for a high horsepower engine can deliver fuel at a maximum average rate on the order of 1000 kilograms per hour, whereas a cryogenic pump for a heavy duty engine can deliver fuel at a maximum average rate of about 100 kilograms per hour. The larger fuel flow capacity requires a pump of considerably larger size and mass, and such a pump has unique mounting and support requirements when installed in a cryogenic vessel compared to smaller pumps. In mobile applications there can be axial, transverse, radial, and rotational loads acting on the pump, which if not constrained properly can lead to fatigue in pump supports that secure the pump to the cryogenic vessel and undue stress on the cryogenic vessel itself.
When a cryogenic pump assembly has its pump portion installed within a cryogenic storage vessel there can be a dead volume of fuel at the bottom of the vessel that is inaccessible to the cryogenic pump. This dead volume represents a cash investment into the operating cost of the cryogenic storage vessel and pump over the entire lifetime of the equipment, since the dead volume is always present when the pump is operating. It is desirable to reduce the dead volume of fuel as much as possible, without unduly increasing the cost of the cryogenic storage vessel and reducing the operating efficiency of the pump.
The state of the art is lacking in techniques for cryogenic storage vessels that securely mount a cryogenic pump assembly with the pump portion on the end that extends into the cryogen space to reduce dead volume and with features for installing and removing the pump assembly without draining the liquefied fuel from the cryogen space.